1. Field of the Invention
The present invention relates to an absorption waste-heat recovery system including a generator for recovering heat by receiving heat medium fluid containing waste heat and concentrating a solution with absorbent dissolved therein and generating steam, a condenser capable of condensing the steam generated from the generator, an evaporator operable to evaporate condensed water condensed by the condenser and an absorber operable to dilute the concentrated solution concentrated by the generator by causing the solution to absorb the steam from the evaporator.
2. Description of the Related Art
In the absorption waste-heat recovery system described above, there is provided an absorption cold/hot water producing apparatus including the generator for concentrating solution with absorbent dissolved therein into a concentrated solution and generating steam, the condenser capable of condensing the steam generated by the generator, the evaporator operable to evaporate condensed water condensed by the condenser and the absorber operable to dilute the concentrated solution concentrated by the generator by causing the solution to absorb the steam generated from the evaporator. In operation, by inputting heat medium fluid containing waste heat to the generator, the system recovers heat in the form of concentration heat of the diluted solution.
With the absorption cold/hot water producing apparatus described above, for production of cold water, steam obtained by concentration-separation at the generator is condensed by the condenser and this condensed water is supplied to the evaporator, in which the condensed water is caused to contact a heat exchanger tube adapted for producing cold water thereby to absorb latent heat of evaporation, so that the water inside the heat exchanger tube is cooled. The generated steam is guided to the absorber to be absorbed into the concentrated solution therein, whereby the concentrated solution concentrated by the generator is diluted. This diluted solution which has been diluted and heated also is cooled inside the absorber and then returned to the generator. On the other hand, for production of warm water, in many cases, the heat contained in the steam heated by the generator and in the concentrated solution is used directly for the purpose of hot water production.
With the absorption waste-heat recovery system having the above-described conventional construction, in order to improve its heat recovery efficiency, the system often employs a double-effect cycle involving two generators, one being a high temperature generator and the other being a low temperature generator. However, it is difficult for the high temperature generator to recover the heat contained in the heat medium fluid sufficiently. Hence, there has been a desire for further improvement in heat recovery efficiency. More particularly, for example, exhaust gas from a heat-electricity co-generating plant generally has a temperature of 200 to 300xc2x0 C. and the diluted solution introduced to the high temperature generator has a temperature of about 150 to 155xc2x0 C. after being pre-heated through heat exchange reaction with the heated concentrated solution. Therefore, there exists the problem of inability to recover the heat of the exhaust gas sufficiently.
Then, in an attempt to improve this heat recovery efficiency, as known from Japanese laid-open patent application gazette No. Hei. 11-304274 for example, there has been proposed to provide the absorption heat recovery system with still another generator, i.e. an auxiliary heat generator, so that the heat medium fluid after heat recovery by the high temperature generator is introduced to this auxiliary heat generator for further recovery of heat therefrom. In the case of the invention described in the above-identified laid-open gazette, this invention utilizes the reverse flow in order to take advantage of the fact that the steam separated by the high temperature generator has a higher temperature than the concentrated solution after the heat recovery by the auxiliary generator. More particularly, an auxiliary low temperature generator is provided for receiving the concentrated solution from the auxiliary generator and this solution is then separated by the high temperature generator and heated with steam and condensed again. That is, the construction employs the double-effect cycle with heat currents crossing each other. And, for production of hot water with this system, the evaporator is deactivated, so that the cooling water running in a cooling tube of the absorber is taken out as hot or warm water.
More particularly, the diluted solution is fed to the auxiliary generator, where the solution is concentrated. And, this concentrated solution is fed to the low temperature generator. A portion of this concentrated solution concentrated by the low temperature generator is fed to the high temperature generator. On the other hand, the concentrated solution fed to the low temperature generator is heated with steam separated by the high temperature generator. Further, the concentrated solution re-concentrated at the high temperature generator is used for preheating a portion of the concentrated solution from the low temperature generator and then fed to the absorber together the remaining portion of the concentrated solution from the low temperature generator. The steam separated at the high temperature generator and having heated the concentrated solution at the low temperature generator, the steam separated at the low temperature generator and the steam separated at the auxiliary generator are guided to the condenser to be cooled and condensed thereat. Condensed water condensed from the steam at the condenser is evaporated at the evaporator, thereby to absorb latent heat of evaporation, thus producing cold water. The concentrated solution concentrated at the high temperature generator and the remaining portion of the concentrated solution concentrated at the low temperature generator are together guided to the absorber to absorb the steam evaporated at the evaporator, so that the resultant heat of absorption heats the cooling water. Here, if the low temperature generator guides the steam from the high temperature generator after heating the concentrated solution from the auxiliary generator directly to the evaporator via a bypass passage, this steam together with the steam from the auxiliary generator and the steam from the low temperature generator are guided to the evaporator, so that warm water may be produced.
As described above, with the invention disclosed by the above-identified laid-open patent application gazette, the cycle is very complicated. And, the heat source represented by a combustion device such as an internal combustion engine will experience variation in the heat amount contained in its exhaust gas containing the waste heat, in association with load variation. In order to allow the concentrated solution and steam to flow from the generators through the respective components to the absorber in accordance with a pressure which is gradually reduced in association with heat exchange reactions between the concentrated solution and the steam, it is necessary to adjust the circulation amount of the solution containing absorbent dissolved therein and also to adjust its pressure relationship. In particular, in the case of the low temperature generator, the concentrated solution from the auxiliary generator is heated with the steam from the high temperature generator. Then, when variations occur in the amount of exhaust gas and its temperature, it is extremely difficult to control the balance between the temperature of the solution to be heated and the heating steam at least at the low temperature generator. This will lead inevitably to complexity in a control mechanism therefor. If the temperature balance is lost, this will lead also to change in the pressure relationship, thus inviting reduction in the output from the heat recovery system. In this way, because of mutual interference present between the high temperature generator and the auxiliary generator, it is believed that the invention of the above-described gazette suffers the problem of extreme difficulity in control conditions and complexity in the controlling system therefor.
In view of the above, a primary object of the present invention is to provide an absorption waste-heat recovery system which effects heat recovery in two steps and which employs an efficient heat recovery cycle utilizing, in combination, a double-effect cycle in which an absorbent has a high saturation temperature and a single-effect cycle in which the absorbent has a relatively low saturation temperature, for greater heat recovery efficiency as well as for greater simplicity of the system construction.
For accomplishing the above-noted object, according to the first feature of the present invention, an absorption waste-heat recovery system comprises:
a high temperature generator for directly receiving a heat medium fluid containing waste heat for recovering heat therefrom and concentrating a solution having an absorbent dissolved therein and generating steam;
a low temperature generator for re-concentrating the concentrated solution concentrated at the high temperature generator after reduction of its temperature by heat recovering means in the system by using the steam from the high temperature generator as heat source;
an auxiliary generator for introducing the heat medium fluid after its heat recovery at the high temperature generator and again recovering heat therefrom;
a condenser capable of condensing steam from the auxiliary generator and steam after the re-concentration of the concentrated solution at the low temperature generator;
an evaporator for evaporating the condensed water condensed at the condenser; and
an absorber for receiving the concentrated solution from the low temperature generator and the concentrated solution from the auxiliary generator and diluting these solutions by causing them to absorb the steam from the evaporator;
wherein a double-effect cycle using the high temperature generator and the low temperature generator and a single-effect cycle using the auxiliary generator share at least the evaporator and the absorber out of the condenser, the evaporator and the absorber.
With the absorbent waste-heat recovery system having the above-described construction, the system is adapted for recovering heat in the two stages, i.e. at the high temperature generator and at the auxiliary generator. Further, the concentrated solution separated at the high temperature generator and the concentrated solution separated at the auxiliary generator are supplied respectively to the absorber via passages thermally insulated from each other. And, the steam separated at the high temperature generator and the steam separated at the auxiliary generator are also supplied respectively to the condenser via passages thermally insulated from each other.
With the above construction of the present invention, by using the double-effect cycle and the single-effect cycle in combination and recovering heat from the heat medium fluid in the two stages of the high temperature generator and the auxiliary generator, the heat contained in the heat medium fluid may be recovered with high efficiency and the control mechanism may be simplified. Moreover, the heat recovered at the high temperature generator and the heat recovered at the low temperature generator acting as heat input units respectively for the double-effect cycle and the single-effect cycle which cycles share at least the evaporator and the absorber out of the condenser, the evaporator and the absorber are not exchanged with each other between the steam and concentrated solution from the high temperature generator containing the former heat and the steam and concentrated solution from the auxiliary generator containing the latter heat. Rather, these steams are supplied respectively to the condenser and the concentrated solutions are supplied respectively to the absorber. Hence, there occurs substantially no interference between the double-effect cycle and the single-effect cycle. As a result, it becomes possible to carry out the control of the circulation amount of diluted solution to the high temperature generator and the control of the circulation amount of diluted solution to the auxiliary generator substantially independently of each other. That is, the steams separated respectively at the high temperature generator and the auxiliary generator are supplied to the condenser via thermally insulated respective passages and also the concentrated solutions separated at the high temperature generator and the auxiliary generator are also supplied to the absorber via thermally insulated respective passages. With these arrangements, even if there occurs a change which may disturb the favorable balance between the heat recovery amount at the high temperature generator and the heat recovery amount at the auxiliary generator, this can be coped with simply by adjusting the circulation amounts of the diluted solutions to the respective generators.
According to the second feature of the present invention, in the system described above, the system further comprises bypass passages for connecting a steam passage from the high temperature generator, a steam passage from the auxiliary generator, a concentrated solution passage from the high temperature generator and a concentrated solution passage from the auxiliary generator respectively via circuit closing means to the absorber, so that by opening the bypass passage with manipulation of the circuit closing means the absorber or the evaporator produces hot water.
With this second feature of the invention, in addition to the function and effect by the first feature, hot or warn water can be readily produced by the system. That is, owing to the inclusion of the bypass passages for connecting a steam passage from the high temperature generator, a steam passage from the auxiliary generator, a concentrated solution passage from the high temperature generator and a concentrated solution passage from the auxiliary generator respectively via circuit closing means to the absorber, if the circuit closing means is opened, the bypass passages are opened up. As a result, all terminal pressures of the steam passage and the concentrated solution passage from the high temperature generator and the steam passage and the concentrated solution passage from the auxiliary generator become equal to a pressure inside the absorber. which would be at its minimum if the bypass passage were closed. Accordingly, substantially all of the concentrated solutions and the steams will flow into the absorber through the respective bypass passages. Consequently, hot or warn water may be produced at a cooling pipe included in the absorber. Alternatively, by transferring its heat to the evaporator, hot or warn water may be produced at the heat exchanger tube included in the evaporator.